The invention relates to a method and a system for shop floor control of work stations, in particular for factory automation. More particularly, it relates to automation of work stations whether or not associated with shop floor outfits.
An individual work station comprises a console intended for an operator and is sometimes associated with peripherals such as bar-code readers. This work station is connected to a shop floor control center, typically including one or more computers associated with data file servers and internal dedicated monitors. A similar work station may be associated with the control computer of a shop floor machine. The unit comprising the machine and the computer provided with its work station comprises an outfit. The set of work stations, whether or not associated with outfits, and connected to the shop floor control center, comprises a shop floor control system for factory automation.
In an outfit, the dialogue between the console of the work station and the computer depends on the software of the computer. It is designed to perform highly specific functions and to make the outfit very powerful. It is, accordingly, ordinarily highly sophisticated. The computer is also provided with a line for communication with the outside. The line is often an asynchronous line. However, the present trend is to equip the computer with a high-output line capable of direct connection with a local area network (LAN). Consequently the possibilities for dialogue offered by the computer communication line are quite variable, ranging from the simplest to the most sophisticated depending on the outfit. At the present time, however, these possibilities are often limited by the presence of only one asynchronous line. The computer may also have a storage unit comprising disks, diskettes or tapes.
The presently most powerful shop floor control system uses a LAN connecting the outfits to the shop floor control center. There are several types of LAN. For example, one well-known type uses the transmission technique known as CSMA/CD (carrier sense multiple access/collision detection), an example being the "Ethernet" network. Its application to industry, however, presents serious disadvantages. In industry, a local area network more recently used is one that uses the token bus technique, an example being the MAP (Manufacturing Automation Protocol) network.
On the subject of the local area network, the ISO (International Standards Organization) has currently defined a model for interconnection of open systems, known as the OSI (open systems interconnect) model, defining 7 layers. The majority of present-day networks, such as those based on the Ethernet network, rely on the low-layer services of the OSI model. The applications typically use the services offered by the fourth layer, known as the transport layer, and the fifth layer, known as the session layer. Finally, the industrial networks, such as the MAP network, are beginning to offer standardized services in the sixth layer, known as the presentation layer, and the seventh and last layer known as the application layer or problem-oriented layer.
Naturally, it would be desirable to be able to connect all the work stations of a shop floor, whether or not they are associated with outfits, to a local area network to obtain very powerful automation of the shop floor. However, the difficulties encountered are major and varied. It is often found that in a large factory, such as one for manufacturing printed circuit boards and assembling components on the boards, existing or planned future outfits are highly heterogenous in terms of the processors, operating systems or internal dedicated monitors. In this case, each outfit presents a specific problem. The addition of individual work stations adds further specific problems.
In a shop floor control system, the individual work stations are connected directly to the shop floor control center. The shop floor control center must directly manage each of the individual work stations. This is a heavy responsibility for the shop floor control center and must be adapted to the number and specificity of the work stations. Because of this management responsibility, it is, for example, impossible to transmit to an individual work station documents in the form of text associated with drawings and/or images, such as complex digitized documents. Yet an individual work station may need such data.
The problems associated with the shop floor control of factory outfits depend on the type of these outfits. They differ depending on whether the outfits are not directly connectable to a LAN, or are directly connectable to or already connected to a LAN.
Since local area networks have only recently been extended to the automation of existing factories, many outfits for these factories have not been designed for connection to a LAN. In an outfit of this type, the computer is simply open to the outside by an asynchronous communication line. This line furnishes a low-output link and must be connected directly to the entire set of file servers of the shop floor control center. Hence the software of all the file servers must be adapted as a function of the outfit connected. This adaptation itself is already time-consuming and expensive. Moreover, the outfits of this type generally have different software and dialogue protocols. Consequently, adding an outfit of a different type requires fundamental modification of the software of all the file servers.
Outfits that are connectable or already are connected to a LAN also present problems in their shop floor control through this LAN. These problems often arise for the shop floor control of outfits of the foregoing type as well. For example, an outfit having a computer not provided with local programs must seek programs in an file server of the shop floor control center. Thus if the file server should malfunction, it blocks all the outfits of this type. On the other hand, the dialogue between the operator and the outside is currently done by menus. The dialogue, thus, often requires a large number of delicate operations and so impairs the productivity of the associated work station.
Other problems are associated with the scale of manufacture of the factory. For a large-series job, the basic programs are normally on disks and the supplementary programs are sent via the communication line to be stored locally on various media (disks or diskettes). The routing thus depends on the quality of the line and above all on its availability. When the shop floor control bears on small series requiring a great number of references, the shop floor control requires a great number of manipulations. This entails numerous non-productive periods and complex management of disks and diskettes as well as updating them are required. It gives rise to the notion of transparency at the level of the files used and presents the general problem of archiving, saving and management of the technical status at each work station or type of work station.